Deoxygenation process

ABSTRACT

A deoxygenation process includes the steps of adding hydrazine to a liquid containing dissolved oxygen, passing the liquid through a bed of activated carbon to catalyze a reaction between the dissolved oxygen and hydrazine whereby carbon contaminants are added to the liquid, and removing the contaminants. In another embodiment, unreacted hydrazine that remains in the liquid following the catalysis is removed by passing the liquid through an ion exchange resin. In still another embodiment, an activated carbon-catalyzed deoxygenation process employing hydrazine is practiced on a mobile platform and the process further includes the steps of transporting the apparatus to a regenerating station for regeneration. The invention also includes apparatus for carrying out the process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to a process for removing dissolved oxygen fromliquids.

2. Background of the Invention

Processes for the removal of dissolved oxygen from liquids haveapplications in many diverse fields. In a number of industries,including those of beverage making, electronics, aerospace, deep wellinjection, and power generation, water is used in great quantities andthe presence of unsatisfactory levels of dissolved oxygen can presentnumerous problems, including inferior product quality and damagedprocess equipment. As one example, dissolved oxygen contained in hotwater that is circulated through power generating equipment and the likeis a major cause of corrosion. Because of the enormous costs ofreplacing corroded power generating equipment parts, unsatisfactorylevels of dissolved oxygen cannot be tolerated.

In prior art deoxygenation processes, hydrazine has been used as astrong reducing agent to prevent corrosion and other problems associatedwith oxygenated water. A small amount of hydrazine is added to the waterto react with the dissolved oxygen to form nitrogen and water. In thefield of power generation, a small amount of hydrazine is also providedin the deoxygenated water as it circulates in the power generatingequipment. The circulating hydrazine and water mixture is said to causethe formation of magnetite on metal surfaces of the equipment by thereaction of hydrazine with iron, and the magnetite in turn helps protectagainst corrosion. Hydrazine also reduces red iron oxide deposits thattypically form in power generating equipment and impede heat transferand cause tubes to rupture. The product of this reduction reaction ismagnetite which will settle to the bottom of a water stream and whichcan thereby be effectively and economically removed from generatingequipment.

It is known that the reaction of hydrazine with dissolved oxygen can becatalyzed by passing the hydrazine and water mixture through a bed ofactivated carbon. Such a catalyzed deoxygenation process is described inF. R. Houghton, et al, "The Use of Activated Carbon With Hydrazine inthe Treatment of Boiler Feedwater", International Water Conference,Bournemouth, England (1957) on pages 54-58, wherein boiler feedwatercontaining between 5 and 7 parts per million of dissolved oxygen isdosed with hydrazine in an amount of from 30 to 70% over thestoichiometric amount necessary to react with the dissolved oxygen. Thedosed water is subsequently passed through a bed of activated carbon andthen fed directly into a boiler.

Despite the advantages that one skilled in the art might expect from thecatalyzation of a deoxygenation reaction, the prior art teachings ofactivated carbon catalysis of hydrazine deoxygenation have been almostcompletely ignored by the art due to a number of disadvantages inherentin the prior art processes.

A first disadvantage of the catalyzed deoxygenation processes of theprior art arises from the introduction of impurities, such as unreactedhydrazine and carbon contaminants, into the deoxygenated liquid. In theprocess of removing dissolved oxygen, the prior art systems leave levelsof unreacted hydrazine that cannot be tolerated when a liquid such aswater is used in certain sophisticated equipment or for the productionof refined products. Among other unsatisfactory effects, unreactedhydrazine can raise the conductivity and the pH of the deoxygenatedwater to unsatisfactory levels. The processes of the prior art alsointroduce carbon contaminants into the deoxygenated liquid and thepresence of these contaminants likewise is intolerable when adeoxygenated liquid of high purity is required. In the field of powergeneration, for example, such impurities render the prior art processesuseless in high pressure equipment and, as a result, the significantbenefits of carbon-catalyzed water deoxygenation have been unavailableto the art.

Even when a certain amount of unreacted hydrazine is desirable in thedeoxygenated water for the purpose of inhibiting corrosion duringcirculation in power generating apparatus, the prior art processes areinadequate in that no provisions are made for effectively adjusting theamount of unreacted hydrazine remaining after deoxygenation in order toprovide the optimum amount of hydrazine in the circulating water. Thus,in selecting an optimum amount of hydrazine to be reacted during thedeoxygenation stage, a residual amount of unreacted hydrazine can resultwhich will be either higher or lower than the optimum amount for thecirculating stage. If the amount during the circulating stage is toolow, the anticorrosive effects of the hydrazine are lost, and if theamount during the circulating stage is too high, the pH and conductivityof the circulating water can be raised to unacceptable levels. Someprior art processes have attempted to remedy this defect when theresidual amount of unreacted hydrazine is too low by simply providing ameans for adding hydrazine before the circulating stage. However, thistype of arrangement fails to remedy the defect when the amount is toohigh and, further, completely fails to allow the flexibility needed toenable one to use a different anti-corrosive agent than hydrazine in thecirculating stage.

Still another shortcoming of the prior art is the failure to fullyappreciate and address the hazards associated with hydrazine. Not onlydoes hydrazine present a severe explosion hazard, especially whenexposed to heat or oxidizing materials, but it is also highly toxic byingestion, inhalation, and even skin absorption, and is a strongirritant to skin and eyes. Unconfirmed reports link hydrazine to cancer.In the prior art, no special precautions have been suggested for thehandling of hydrazine used in deoxygenation processes nor for thehandling of material beds that contain hydrazine.

Thus, there is a long-felt and unresolved need for an improvedcarbon-catalyzed deoxygenation process employing hydrazine that can beused commercially in a variety of applications. Ideally, the processwould secure for the art all of the advantages that catalyzation of areaction normally provides without prohibiting its use due to all of theincumbent disadvantages discussed hereinabove. To the fulfillment ofthis need and to other objectives that will become apparent from thefollowing, the present invention is directed.

SUMMARY OF THE INVENTION

This invention is a deoxygenation process that includes the steps ofadding hydrazine to a liquid containing dissolved oxygen, passing theliquid through a bed of activated carbon to catalyze a reaction betweenthe dissolved oxygen and hydrazine whereby carbon contaminants are addedto the liquid, and removing the contaminants. In another embodiment,unreacted hydrazine that remains in the liquid following the catalysisis removed by passing the liquid through an ion exchange resin. In stillanother embodiment, an activated carbon-catalyzed deoxygenation processemploying hydrazine is practiced on a mobile platform and the processfurther includes the steps of transporting the apparatus to aregenerating station for regeneration. The invention also includesapparatus for carrying out the process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram depicting an apparatus in accordance withthe invention.

FIG. 2 is a schematic diagram depicting an apparatus in accordance witha second embodiment of the invention, wherein a bypass is providedaround one or more vessels.

FIG. 3 is a schematic diagram depicting an apparatus in accordance witha third embodiment of the invention, wherein the invention includes anenclosed, mobile platform.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As depicted in FIG. 1, the invention includes a conduit 12 that has aninlet 14 for receiving a stream of liquid containing dissolved oxygenand an outlet 16 for discharging liquid that has been deoxygenated. Theconduit communicates with vessels 18 connected in parallel andcontaining activated carbon 20, so that liquid flowing through conduit12 passes through the carbon as indicated by the arrows adjacent to thevessels. The conduit also communicates with vessels 22 that areconnected in parallel and contain ion exchange resin 24, so that liquidflowing through the conduit also passes through the ion exchange resin.Before liquid passing through the conduit contacts the activated carbon,hydrazine 26 is pumped into the liquid from hydrazine tank 28 by meansof hydrazine pump 30.

The liquid that is introduced into inlet 14 is demineralized orundemineralized and has a dissolved oxygen content of up to thesaturation point of oxygen in the liquid for the prevailing temperatureand pressure conditions. The liquid temperature can vary widely fromjust above the liquid's freezing point to a temperature that is justbelow the temperature at which the ion exchange resin would be damaged.

Hydrazine can be added through hydrazine pump 30 in a pure form or in anaqueous solution, but a solution is preferred in order to reduce oreliminate the explosion and fire hazards associated with concentratedhydrazine. Catalyzed or uncatalyzed hydrazine can be employed withbeneficial results. Preferably, uncatalyzed hydrazine is used because ofits lesser cost. Also, in the case of certain sophisticated powergenerating apparatus such as nuclear power generators, catalyzedhydrazine can cause residual catalysts such as cobalt to remain in thedeoxygenated water and such catalysts can damage the generatingapparatus. In a preferred embodiment, Scav-ox, a 35% aqueous solution ofuncatalyzed hydrazine distributed by Olin Chemical Company, is used.

Hydrazine pump 30 is any conventional means for dispensing a measuredamount of fluid. The interior surfaces of the pump, as well as conduits32 and 34 which are contacted by the hydrazine solution, are selectedfrom materials such as stainless steel that are not damaged by thestrong reducing property of the hydrazine.

It is necessary only to use enough hydrazine to completely react withthe dissolved oxygen contained in the liquid. It has been found, in thepresent invention, that hydrazine in an amount of only about 10 to about20% more than a stoichiometric amount is needed to completely react withthe oxygen. By reducing the amount of hydrazine necessary to practicethe invention, relative to prior art processes, a significant advantageis realized in that the cost of the hydrazine is reduced and lesshydrazine needs to be handled so that the dangers associated therewithare reduced.

It is important that no processing apparatus that would eliminate thehydrazine is disposed between the point 36 at which hydrazine is addedto conduit 12 and activated carbon beds 18. The mixture of hydrazine andliquid is passed through activated carbon 20 to catalyze the reactionbetween the dissolved oxygen and hydrazine. The activated carbon can beany commercially available activated carbon and in a preferredembodiment WV-G activated carbon distributed by Westvaco of Covington,Va. is used.

As a result of the mixing of the liquid with hydrazine and thesubsequent contact with the carbon beds, the deoxygenated liquid leavingvessels 18 typically contains an amount of unreacted hydrazine andcarbon contaminants. The unreacted hydrazine is present because anexcess over the stoichiometric amount of hydrazine is beneficiallyreacted with the liquid, as indicated above. Also, because the dissolvedoxygen content of the incoming liquid may vary, as when the liquid iswater from a storage tank or utility source, the amount of unreactedhydrazine will vary when a fixed amount of hydrazine, unresponsive tothe varying dissolved oxygen content, is added at point 36.

The carbon contaminants are present because the liquid washes them fromthe carbon bed as it passes through. The carbon contaminants can includea wide variety of substances that are detrimental when a high qualitydeoxygenated liquid is required. Many carbonaceous raw materials, suchas wood, coal, nutshells, and petroleum coke, are used for themanufacture of activated carbon and the contaminants vary depending uponthe raw material used. Regardless of which raw material is used, thecontaminants are likely also to include carbon fines.

When the end use of the deoxygenated liquid requires that the unreactedhydrazine be removed, ion exchange resin 24 is selected from the groupconsisting of mixed bed resin and cation resin. If a mixed bed resin isemployed, it consists of any commercially available strong acid cationexchange resin, such as Ionac C-249, and any commercially availablestrong base anion exchange resin, such as Ionac ASB-1. The Ionac resinsare manufactured by Sybron Corporation of Birmingham, N.J. If a cationexchange resin alone is used, it is any commercially available strongacid cation exchange resin such as Ionac C-249.

Ion exchange resin 24 typically does not filter out all of the carbonfines contained in the deoxygenated water. To effect their removal,filter 38 containing filter media 40 is disposed in communication withconduit 12 between vessels 22 and outlet 16. The size of the filtermedia particles is selected to prevent passage of the fines, and it hasbeen found that a media particle size of 100 microns or less is suitablefor this purpose. In a preferred embodiment, at least some of the carbonfines are also removed by pre-washing the activated carbon. Theactivated carbon can be prewashed with water that has not beendemineralized, but the minerals of the water are typically adsorbed bythe carbon and can be released as contaminants when the deoxygenationprocess is practiced. Preferably, the pre-wash is undertaken withdemineralized water to eliminate this problem.

From the foregoing, it will be appreciated that by selecting a mixed bedresin, both the unreacted hydrazine and certain of the carboncontaminants are removed. Thus, when the end use requires the removal ofboth hydrazine and contaminants, the use of a mixed bed resin ispreferred. For similar reasons, another embodiment involves the use of acation resin vessel and an anion resin vessel in a series relationshipand in communication with conduit 12 downstream of vessels 18.

In accordance with the invention depicted in FIG. 1, both the unreactedhydrazine and carbon contaminants are economically and efficientlyremoved. Even in certain applications where a predetermined amount ofunreacted hydrazine in the deoxygenated liquid is desirable, thecomplete removal of hydrazine in accordance with the present inventionis beneficial because it is then possible to add the desired amount ofhydrazine without the need for constantly monitoring the amount ofresidual hydrazine from the deoxygenation process and compensatingtherefor. In the field of power generation, the complete removal ofhydrazine is also advantageous when it is desired to use ananti-corrosive agent for circulating through the generating apparatusthat is different from hydrazine.

FIG. 2 depicts an embodiment which offers an alternative to firstremoving all of the unreacted hydrazine and then adding back the desiredamount. In this embodiment, hydrazine 42 is pumped by pump 44 intoconduit 46 where it is mixed with water containing dissolved oxygen. Thewater and hydrazine are passed through vessels 48 which containactivated carbon 50, and the amount of hydrazine remaining in solutionafter leaving vessels 48 is measured by chemical analyzer 50. Theanalyzer regulates valve 52 such that, when the amount of unreactedhydrazine is greater than the amount ultimately desired in the effluent,the valve diverts at least a percentage of the water from bypass conduit56 through ion exchange resin 54. The hydrazine in the percentagedirected through resin 54, contrary to that in the percentage directedthrough conduit 56, is removed and by regulating the amounts of the twopercentages, the amount of hydrazine remaining per unit volume ofeffluent at point 58, where the two percentages are recombined, isefficiently and precisely regulated.

When the amount of unreacted hydrazine detected by analyzer 50 is lessthan the amount ultimately desired in the effluent, second hydrazinepump 60 can be energized by analyzer 50 to introduce a quantity ofhydrazine 62 sufficient to arrive at the ultimately desired amount.However, the need for adding hydrazine is preferably eliminated byadding a sufficient amount of hydrazine 42 such that there will alwaysbe an amount detected by analyzer 50 that is equal to or greater thanthat ultimately desired.

The hazards of hydrazine have been noted above and certain of thesehazards remain even where hydrazine is present in a dilute aqueoussolution. For example, when a hydrazine solution is passed through anactivated carbon bed and ion exchange resin beds, a residue of unreactedhydrazine can remain in the beds and handling of the beds can causehealth hazards. When such handling is done by inexperienced persons atthe site where the deoxygenated liquid is needed, the health hazards aremultiplied.

In the embodiment depicted in FIG. 3, the hazards associated with theuse of hydrazine in a deoxygenation process have been reduced oreliminated. In this embodiment, apparatus for deoxygenating water isdisposed on a mobile, enclosed platform 64.

The apparatus contained on the mobile platform is similar to thatdepicted in FIG. 1. In FIG. 3, the apparatus includes a conduit 68 forcarrying water that initially contains dissolved oxygen. The conduit hasan inlet 70 which is releasably attached to a water supply and an outlet72 which is releasably connected to a power generating apparatus 74.After being introduced into the conduit, feed water passes to one end ofthe platform and hydrazine 76 is pumped into conduit 68 by pump 78. Thewater and hydrazine mixture is then passed through vessel 80 whichcontains activated carbon 82. Then, the water passes through vessels 84which contain cation exchange resin beds 86 and through vessels 88 whichcontain anion exchange resin beds 90 to remove any unreacted hydrazineand carbon impurities and to demineralize the feed water. The water isthen passed through vessel 92 which contains a polisher 94. Adjacent tooutlet 72, hydrazine 96 contained in a second hydrazine container 98 canbe added to the feed water by means of hydrazine pump 100. Since nounreacted hydrazine remains in the feed water at the point at which pump100 communicates with conduit 68, apparatus for measuring the unreactedhydrazine content is unnecessary and an amount of hydrazine can beuniformly added which is optimum for use in the circulation stage.Filter 108 removes carbon fines that pass through the ion exchange resinbeds.

Numerous advantages flow from the arrangement of the parts of theinvention depicted in FIG. 3. To begin with, the mobile, enclosedplatform 64 allows the structure embodying the hydrazine and relatedapparatus to be set apart from the main structure that houses the powergenerating apparatus. In this fashion, hazards associated with thehydrazine are minimized.

Another important feature of the embodiment depicted in FIG. 3 is thatplatform 64 is mobile. Thus, after an amount of water has beendeoxygenated and the activated carbon and resins need to be regeneratedor replaced, the trailer can be transported to a regeneration station,where specialized equipment and employees can regenerate the apparatuswith minimal risks. In this way, employees at the power generating plantor other site of use avoid contact with hydrazine fumes and hydrazinedeposits remaining in the activated carbon and other resins.

The following examples specifically illustrate the practice of thepresent invention. Suitable vessels, valves, conduits and accessoryequipment for practicing the present invention are described in U.S.Pat. No. 4,383,920, and said patent is hereby incorporated by reference.

EXAMPLE 1

In accordance with the present invention, oxygen is removed from atwo-step demineralizer effluent containing about 8 to 10 parts permillion of dissolved oxygen. The effluent is introduced at a rate of 110to 540 gallons per minute, usually 500 GPM, into an apparatus comprisinga hydrazine pump, six activated carbon tanks connected in parallel, andsix mixed bed tanks connected in parallel.

A 35% solution of hydrazine is added to the effluent at a ratio of 0.4gallons per hour of hydrazine solution per 100 GPM of effluent. Duringthe first 3.5 hours, the system yields a product having less than 0.1ppm dissolved oxygen and the feed rate of the hydrazine solution isgradually reduced to 0.2 GPH per 100 GPM effluent. After 36 hours ofsuccessful performance at this feed rate, the rate is gradually reducedto 0.15 GPH of hydrazine solution. In this example it has been foundthat, on average, the introduction of about 8.9 ppm of hydrazine to theeffluent is sufficient.

After introduction of the hydrazine solution, the effluent is thenpassed through the activated carbon tanks. Each tank contains a 60 cubicfoot bed of activated carbon for a total of 360 cubic feet of carbon.The effluent is then passed through the mixed bed tanks, each of whichcontains 96 cubic feet of mixed bed resin for a total of 576 cubic feet.

The demineralized and deoxygenated product of Example 1 is found tocontain less than 10 ppb dissolved oxygen and less than 1 ppb hydrazine.After a lengthy shutdown, dissolved oxygen content was found to berelatively high upon restart but this increased content was eliminatedby temporarily increasing the feed rate of hydrazine.

EXAMPLE 2

In accordance with the present invention, oxygen is removed from eithercondensate or dimineralized makeup water containing from 0.5 ppb to 10ppm dissolved oxygen and having a conductivity of 1 micromho. Theinfluent is treated in an apparatus comprising a hydrazine pump, threeactivated carbon tanks connected in parallel, three mixed beds alsoconnected in parallel, and a continuous oxygen monitor.

Influent is introduced into the apparatus at the rate of 130 to 470 GPM.The oxygen level of the influent varies and is high (several ppm) whentreating demineralized makeup water and low (less than 1 ppm) whentreating condensate.

A 35% solution of hydrazine is pumped into the influent stream upon itsintroduction into the apparatus. The flow rate of hydrazine solution is0.2 GPH per 100 GPM of influent for the first 24 hours. Then, the flowrate is gradually diminished over the second 24 hour period to a minimumof 0.02 GPH per 100 GPM of 1 ppm dissolved oxygen stream. Thestoichiometric relationship is 0.017 GPH of hydrazine solution per 100GPM of an influent containing 1 ppm dissolved oxygen.

After hydrazine is introduced into the influent feed, the mixture ispassed through the three activated carbon tanks. Each tank contains 60cubic feet of activated carbon for a total of 180 cubic feet. Thecondensate is then passed through the three mixed beds, each of whichcontains 96 cubic feet of mixed bed resins for a total of 288 cubicfeet. A continuous dissolved oxygen monitor measures the amount ofdissolved oxygen in the treated effluent and the effluent is thentransferred to a storage tank. The treated effluent is found to contain2 to 19 ppb of dissolved oxygen. The conductivity of the influent whichis 6 micromhos following passage through the carbon tanks, is reduced toless than 1 micromho, typically 0.2 micromho, after passage through themixed beds.

Having thus described the present invention in detail, it will beapparent to those skilled in the art that modifications and additionscan be made which are within the spirit and scope of the invention.

We claim:
 1. A deoxygenation process comprising a first step of addinghydrazine to a liquid containing dissolved oxygen, a second step ofpassing said liquid through a bed of activated carbon to catalyze areaction between said dissolved oxygen and said hydrazine whereby anamount of dissolved carbon contaminants are added to said liquid, and athird step of passing said liquid through an ion exchange resin selectedfrom the group consisting of mixed bed resin and cation resin to removeat least said dissolved contaminants.
 2. The deoxygenation process ofclaim 1, wherein an amount of undissolved contaminants are also addedduring said second step and said process further comprises a fourth stepof passing said liquid through a filter media after said second stepwhereby at least said undissolved contaminants are filtered from saidliquid.
 3. The process of claim 1, further comprising the step ofbackwashing said activated carbon before said first step to reduce saidamount of carbon contaminants.
 4. The process of claim 3, wherein saidbackwashing step comprises backwashing with demineralized water.
 5. Theprocess of claim 1, wherein, after said second step, an amount ofunreacted hydrazine remains in said liquid, and wherein said unreactedhydrazine is removed in said third step.
 6. The process of claim 1,wherein said liquid is water.
 7. The process of claim 6, furthercomprising the final step of circulating said deoxygenated water atelevated temperatures in a power generating apparatus.
 8. Adeoxygenation process comprising a first step of adding hydrazine to aliquid containing dissolved oxygen, a second step of passing said liquidthrough a bed of activated carbon to catalyze a reaction between saiddissolved oxygen and said hydrazine whereby an amount of unreactedhydrazine remains in said liquid following said second step, and thethird step of passing said liquid through an ion exchange resin selectedfrom the group consisting of mixed bed resin and cation resin to removeat least a portion of said unreacted hydrazine.
 9. The process of claim8, wherein said liquid is water.
 10. The process of claim 9, furthercomprising the final step of circulating said deoxygenated water atelevated temperatures in a power generating apparatus.
 11. Adeoxygenation process for providing a liquid having a predeterminedamount of unreacted hydrazine comprising a first step of addinghydrazine to a liquid containing dissolved oxygen, a second step ofpassing said liquid through a bed of activated carbon to catalyze areaction between said dissolved oxygen and said hydrazine whereby anamount of unreacted hydrazine remains in said liquid following saidsecond step, a third step of providing an ion exchange resin selectedfrom the group consisting of mixed bed resin and cation resin and abypass conduit that bypasses said resin, and a fourth step of passingsaid liquid through said bypass conduit and diverting at least a portionof said liquid from said conduit to pass through said resin when saidliquid contains more hydrazine than said predetermined amount.
 12. Theprocess of claim 11, further comprising a fifth step of adding hydrazineto said liquid from said second step when said liquid from said secondstep contains less hydrazine than said predetermined amount.
 13. Theprocess of claim 11, wherein said liquid is water.
 14. The process ofclaim 13, further comprising the final step of circulating said water atelevated temperatures in a power generating apparatus.
 15. Adeoxygenation process comprising a first step of adding hydrazine to aliquid containing dissolved oxygen, a second step of passing said liquidthrough activated carbon to catalyze a reaction between said dissolvedoxygen and said hydrazine, and a third step of substantially completelyremoving said hydrazine by passing said liquid through an ion exchangeresin selected from the group consisting of mixed bed resin and cationresin.
 16. The process of claim 15, wherein said liquid is water. 17.The process of claim 16, further comprising the final step ofcirculating said water at elevated temperatures in a power generatingapparatus.
 18. The process of claim 17, wherein, before said final step,a predetermined amount of a corrosion inhibiting substance is added tosaid water.